How to purchase and count the labor type products?

Dear Gurus,

This is the scenario.

I send out my products to my supplier for painting. the supplier only paints on my products and send them back partially.

the quantity has to be counted before and after in order to know how many are sent and how many are left.

I tried the service type purchase but it does not show the quantity.

what is the best way to purchase these type of labor?

thank you in advance.